Co-Authors:
Milford H. Marchant Jr., M.D.; Thomas P. Vail, M.D.; Steven A. Olson, M.D.
July 2006
Femoroacetabular Impingement (FAI)
- Descriptive Diagnosis characterized by a combination of clinical signs, symptoms, and pathology
that may be responsible for the progression of degenerative changes in patients with osteoarthritis of the hip
- Distinct Mechanical entity defined as the abutment between the proximal femur and the acetabular rim.
Relation to Hip Arthritis
- Types of Mechanical Arthritis
- Osteoarthritis - Primary Idiopathic
- Secondary (Trauma, Development Dysplasias)
- Etiology
- Prior Biomechanical theories suggest that cartilage damage is initiated by Concentric or Eccentric overload.
- Eccentric overload
- easily explained by non-congruent articulations caused by developmental dysplasias and post-traumatic anatomy
- Concentric overload
- not as easy to explain
-
Harris. CORR. 1986.
- Large Majority of cases previously thought to be primary or idiopathic osteoarthritis (OA)
are actually secondary to unrecognized mild developmental abnormalities
- Review of 75 patients with idiopathic OA, 79% had subtle abnormal femoral or acetabular
morphology
- Femoral deformity
- Abnormal head/neck contour
- Slipped Epiphysis, Legg-Calve-Perthes
- More Common in Males - later onset (70’s)
- Acetabular dysplasia
- Coxa profunda / Retroversion
- More Common in Females - earlier onset (60’s)
- Fails to completely explain the development of arthritis is patients with non-dysplastic appearing skeletal structures
-
Ganz et al. CORR. 2003.
- Summarized the concept of FAI
- Mechanism for development of osteoarthritis based on subtle aberrant bony morphology
- Acetabular Retroversion / Coxa Profunda
- Femoral Head non-sphericity
- Abnormal Contact in Normal / Near Normal Appearing Hips
- Abutment of the Proximal Femur on the Acetabular Rim during terminal motion of the hip
leading to lesions of the labrum and/or the adjacent cartilage
- Chondral and Labral lesions progress and result in degenerative disease
-
Leunig et al. CORR. 2004.
- Acetabular Rim degeneration & early hip arthritis
- 30 cadavers and 18 hemiarthroplasty patients for displaced femoral neck fractures (Ages > 60)
- No patients with radiographic evidence of OA
- 30/30 cadavers had labral and acetabular cartilage damage
- 17/18 patients with labral injury and 16/18 with acetabular cartilage injury
- All but 1 femoral head cartilage was normal
- 80% found to have evidence of FAI
- Acetabular Rim Degeneration is a constant finding in the aged hip and FAI may be a significant trigger
Biomechanics:
- Impingement
- Normal / Near-Normal hips
- Impingement occurs at excessive or supraphysiologic ranges of motion = Flexion / Adduction / Internal Rotation
- Minor Trauma
- Specific occupations (Carpet Layers)
- Atypical Bony Morphology
- Less motion is required for impingement
- 2 Mechanisms for FAI
- CAM Impingement
- Pincer Impingement
-
CAM Impingement
- Anatomy
- Abnormal Femoral Head/Neck junction with increased radius at the waist
- Motion
- Impingement occurs primarily during flexion, adduction, IR
- Mechanics
- Contact between the femoral neck and acetabular rim induces compression
- Shear stress generated at the junction between the labrum and the cartilage and at the subchondral tidemark
- Outward avulsion of the labrum and/or an inward compression of the articular cartilage at Anterosuperior Rim
- Etiology of CAM Impingement
- Elliptical Femoral Head
- Slipped Capital Femoral Epiphysis -
SCFE:
-
Legg Calve Perthes:
-
Adult Osteonecrosis:
- Malunited Femoral Neck Fractures
-
Pincer Impingement:
- Anatomy
- Excessive Acetabular Coverage
- Motion
- Dependent on acetabular morphology
- Mechanics
- Linear Contact between the labrum and femoral head/neck junction
- Anterior = Acetabular Retroversion
- Circumferential = Coxa Profunda
- Force from the femoral neck is transferred through the labrum to the acetabular cartilage
- Results is chronic degeneration of anterior labrum and subsequent ossification
- Further deepens the cup
- Resultant leverage of head in acetabulum with excessive ROM can result in contre-coup lesion
in posteroinferior acetabulum and posteromedial femoral head
- Leading to Circumferential involvement
- Etiology
- Acetabular Retroversion
-
Coxa Profunda:
-
Protrusio Acetabuli:
- Iatrogenic overcorrection for retroversion/dysplasia
-
Coxa Vara:
- Os Acetabuli
- CAM and Pincer mechanisms produce differing mechanisms for labral injury
- CAM
